Screens not going to sleep after configured time when session is locked

I noticed that when I lock the session the screen does not ever go to sleep. So after searching the forum, I found this answer and placed it into a little script. The only change I made was not passing a session number (which should then take effect on the current session according to loginctl(1)).

Anyway, this activates immediately upon locking the session that the screens turn off. Why then this question?

Alas, eventually the screens will come back from sleep and I don’t know why or how. I have so far tried to rule out the mouse (by disconnecting it before locking the session) but have run out of ideas.

That’s the reason I ask here: in locked session state, after the screens awake from sleep (with session locked) why don’t they automatically return to sleep?

NB: apparently the screen sleep mechanism works as configured when the session is not locked.

$ inxi -GS --no-host
  Kernel: 6.6.26-1-MANJARO arch: x86_64 bits: 64
  Desktop: KDE Plasma v: 5.27.11 Distro: Manjaro Linux
  Device-1: AMD Ellesmere [Radeon Pro WX 7100] driver: amdgpu v: kernel
  Display: x11 server: X.Org v: 21.1.12 driver: X: loaded: amdgpu
    unloaded: modesetting dri: radeonsi gpu: amdgpu resolution:
    1: 2560x1440~60Hz 2: 2560x1440~60Hz 3: 1920x1080~60Hz
  API: EGL v: 1.5 drivers: radeonsi,swrast platforms: x11,surfaceless,device
  API: OpenGL v: 4.6 compat-v: 4.5 vendor: amd mesa v: 24.0.2-manjaro1.1
    renderer: AMD Radeon Pro WX 7100 Graphics (radeonsi polaris10 LLVM 16.0.6
    DRM 3.54 6.6.26-1-MANJARO)
  API: Vulkan v: 1.3.279 drivers: radv surfaces: xcb,xlib